秒杀优化

基于Redis完成秒杀资格判断

改进秒杀业务，需求：

1. 新增秒杀优惠券同时，将优惠券信息保存到Redis中
2. 基于Lua脚本，判断秒杀库存、一人一单，决定用户是否抢购成功
3. 如果抢购成功，将优惠券id和用户id封装后存入阻塞队列
4. 开启线程任务，不断从阻塞队列中获取信息，实现异步下单功能 ```lua — 1.参数列表 — 1.1.优惠券id local voucherId = ARGV[1] — 1.2.用户id local userId = ARGV[2]

— 2.数据key — 2.1.库存key local stockKey = ‘seckill:stock:’ .. voucherId — 2.2.订单key local orderKey = ‘seckill:order:’ .. voucherId

— 3.脚本业务 — 3.1.判断库存是否充足 get stockKey if(tonumber(redis.call(‘get’, stockKey)) <= 0) then — 3.2.库存不足，返回1 return 1 end — 3.2.判断用户是否下单 SISMEMBER orderKey userId if(redis.call(‘sismember’, orderKey, userId) == 1) then — 3.3.存在，说明是重复下单，返回2 return 2 end — 3.4.扣库存 incrby stockKey -1 redis.call(‘incrby’, stockKey, -1) — 3.5.下单（保存用户）sadd orderKey userId redis.call(‘sadd’, orderKey, userId)

return 0

<a name="zNuZS"></a>
## 基于阻塞队列实现异步下单
```lua
    private static final DefaultRedisScript<Long> SECKILL_SCRIPT;
    static {
        SECKILL_SCRIPT = new DefaultRedisScript<>();
        SECKILL_SCRIPT.setLocation(new ClassPathResource("seckill.lua"));
        SECKILL_SCRIPT.setResultType(Long.class);
    }
    private BlockingQueue<VoucherOrder> orderTasks = new ArrayBlockingQueue<>(1024 * 1024);
    private static final ExecutorService SECKILL_ORDER_EXECUTOR = Executors.newSingleThreadExecutor();
    @PostConstruct
    private void init(){
        SECKILL_ORDER_EXECUTOR.submit(new VoucherOrderHandler());
    }
    private class VoucherOrderHandler implements Runnable{
        @Override
        public void run() {
            while(true){
                try {
                    VoucherOrder voucherOrder = orderTasks.take();
                    createVoucherOrder(voucherOrder);
                }catch(Exception e){
                    log.error("处理订单异常", e);
                }
            }
        }
    }
    @Override
    public Result seckillVoucher(Long voucherId) {
        Long userId = UserHolder.getUser().getId();
        long orderId = redisIdWorker.nextId("order");
        // 1.执行lua脚本
        Long result = stringRedisTemplate.execute(
                SECKILL_SCRIPT,
                Collections.emptyList(),
                voucherId.toString(), userId.toString(), String.valueOf(orderId)
        );
        int r = result.intValue();
        // 2.判断结果是否为0
        if (r != 0) {
            // 2.1.不为0 ，代表没有购买资格
            return Result.fail(r == 1 ? "库存不足" : "不能重复下单");
        }
        //2.2 为0，有购买资格，把下单信息保存到阻塞队列
        VoucherOrder voucherOrder = new VoucherOrder();
        //2.3 订单id
        voucherOrder.setId(orderId);
        //2.4 用户id
        voucherOrder.setUserId(userId);
        //2.5代金券id
        voucherOrder.setVoucherId(voucherId);
        //2.6放入阻塞队列
        orderTasks.add(voucherOrder);
        return Result.ok(orderId);
    }
    private void createVoucherOrder(VoucherOrder voucherOrder) {
        Long userId = voucherOrder.getUserId();
        Long voucherId = voucherOrder.getVoucherId();
        // 创建锁对象
        RLock redisLock = redissonClient.getLock("lock:order:" + userId);
        // 尝试获取锁
        boolean isLock = redisLock.tryLock();
        // 判断
        if (!isLock) {
            // 获取锁失败，直接返回失败或者重试
            log.error("不允许重复下单！");
            return;
        }
        try {
            // 5.1.查询订单
            int count = query().eq("user_id", userId).eq("voucher_id", voucherId).count();
            // 5.2.判断是否存在
            if (count > 0) {
                // 用户已经购买过了
                log.error("不允许重复下单！");
                return;
            }
            // 6.扣减库存
            boolean success = seckillVoucherService.update()
                    .setSql("stock = stock - 1") // set stock = stock - 1
                    .eq("voucher_id", voucherId).gt("stock", 0) // where id = ? and stock > 0
                    .update();
            if (!success) {
                // 扣减失败
                log.error("库存不足！");
                return;
            }
            // 7.创建订单
            save(voucherOrder);
        } finally {
            // 释放锁
            redisLock.unlock();
        }
    }